Glass-like polysaccharides comprise a class of physically modified polysaccharides. Unlike their native, crystalline counterpart, glass-like polysaccharides are substantially amorphous and comprise glass-like characteristics. Moreover, glass-like polysaccharides substantially lack an organized crystalline pattern. Glass-like polysaccharides have found use in a variety of applications. Such polysaccharides are taught as being useful for abrading surfaces.
Glass-like polysaccharides have also been described as being useful in a variety of food related applications. More specifically, they have been used to encapsulate organoleptic additives. Moreover, glass-like polysaccharides have been described as being useful as water absorbent materials.
Glass-like polysaccharides are typically produced by means of extrusion processes. A typical extrusion process comprises an extrusion vessel fitted with one or more rotating screws. The rotating screw(s) convey, pump or knead the polysaccharide along the screw to a die.
A variety of extruder configurations/designs are known in the art. A “Single Screw Extruder” (SSE) is typically characterized by an extrusion vessel fitted with one rotating screw. The screw is typically machined as a single piece. The SSE design is suitable in applications where a laminar, regular flow or low shear environment is desired. However, the SSE design is less suitable in applications typically requiring high shearing rates.
The “Twin Screw Extruder” (TSE) design is typically characterized by an extrusion vessel fitted with a pair of substantially parallel, independently rotating screws. The pair of screws may be either co-rotating or counter rotating, the co-rotating screw design being more prevalent in view of its “self-wiping” characteristics. The treaded surface defines an alternately disposed helicoidal ridge and groove. The respective treaded surfaces of a first and a second screw are intermeshed. In this way, the ridge of a first screw will typically be received by the groove of the second screw. Likewise, the groove of the first screw receives the ridge of the second screw. TSE screws typically comprise mobile block elements, each block element performing its proper function. The presence of such mobile block elements allows for a vast number of screw designs. The TSE design is suitable in applications where high shearing rates are required. However, since a TSE dissipates more shear energy compared to a SSE, it is less suitable for shear sensitive applications such as for the manufacture of unexpanded glass-like polysaccharides.
The use of extruders comprising both twin screw and single screw sections for compounding thermoplastic starch have been previously reported by Bastiolli et al. (U.S. Pat. No. 6,277,899; U.S. Pat. No. 5,874,486; U.S. Pat. No. 5,569,692; U.S. Pat. No. 5,462,982; U.S. Pat. No. 5,412,005; U.S. Pat. No. 5,384,170; U.S. Pat. No. 5,334,634; and U.S. Pat. No. 5,234,977). However, the use of high boiling plasticizers makes their removal from the final product difficult, often resulting in glass-like polysaccharides comprising a rubbery state.
The manufacture of unexpanded glass-like polysaccharides has been disclosed by Van Lengerich (U.S. Pat. No. 5,972,404; U.S. Pat. No. 6,096,363; U.S. Pat. No. 6,004,594; U.S. Pat. No. 6,436,453; U.S. Pat. No. 6,468,568; U.S. Pat. No. 6,500,463; U.S. Pat. No. 6,723,358; U.S. Pat. No. 6,190,591; U.S. App. 2002/0044968 A1). However, the glass-like polysaccharides taught by Van Lengerich were not disclosed as having any significant absorbent characteristics.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.